1. Field of the Invention
The present invention relates to a structure of a display device for enhancing a contrast ratio.
2. Description of the Related Art
A display device which is very thin and lightweight as compared to a conventional cathode-ray tube display device, a so-called flat panel display, has been developed. A liquid crystal display device having a liquid crystal element as a display element, a light-emitting device having a self-light-emitting element, an FED (field emission display) using an electron beam, and the like compete in the market of flat panel displays. Therefore, lower power consumption and a higher contrast ratio are demanded in order to increase the added value and differentiate from other products.
In general, a liquid crystal display device is provided with one polarizing plate over each of substrates to keep a contrast ratio. When black display is performed more clearly, the contrast ratio can be improved. Therefore, higher display quality can be provided when an image is seen in a dark room such as a home theater room.
For example, it is suggested that a first polarizing plate is provided outside a substrate on a viewing side of a liquid crystal cell, a second polarizing plate is provided outside a substrate facing the substrate on the viewing side, and a third polarizing plate is provided for enhancing the polarization degree when light from an auxiliary light source provided on the substrate side polarizes through the second polarizing plate and passes through the liquid crystal cell, in order to improve a contrast ratio and suppress unevenness of display which is caused due to shortage of the polarization degree and polarization distribution of polarizing plates (see Patent Document 1). [Patent Document 1] PCT International Publication No. 00/34821